1939
* September 1: Germany invades Poland, starting World War II.
* September 3: Britain and France declare war on Germany.
* September 17: Soviet Union invades Poland from the east.
* October 28: Germany and the Soviet Union sign the Molotov-Ribbentrop Pact, dividing Poland between them.
* November 30: Soviet Union invades Finland, starting the Winter War.
1940
* April 9: Germany invades Denmark and Norway.
* May 10: Germany invades Belgium, the Netherlands, and Luxembourg.
* May 26: France surrenders to Germany.
* June 10: Italy declares war on France and Britain.
* June 22: France signs an armistice with Germany, dividing the country into occupied and unoccupied zones.
* July 10: Battle of Britain begins.
* September 15: Battle of Britain ends with a British victory.
* October 28: Italy invades Greece.
1941
* June 22: Germany invades the Soviet Union, starting Operation Barbarossa.
* July 7: Japan attacks Pearl Harbor, bringing the United States into World War II.
* December 7: Japan attacks Pearl Harbor, bringing the United States into World War II.
* December 11: Germany and Italy declare war on the United States.
1942
* January 27: Battle of Bataan begins.
* April 9: Bataan Death March begins.
* May 6: Battle of Coral Sea begins.
* June 5: Midway Island invaded by Japan.
* June 6: D-Day: Allied forces land in Normandy, France.
* August 6: United States drops an atomic bomb on Hiroshima, Japan.
* August 9: United States drops an atomic bomb on Nagasaki, Japan.
* August 14: Japan surrenders to the Allies, ending World War II.
1945
* April 25: United Nations Charter signed in San Francisco.
* October 24: Nuremberg Trials begin.
* December 11: Japanese war criminals executed.